Halogen additives, such as those based on fluorine, chlorine, and bromine, have been used to give flame retardant properties to TPU compositions. In recent years, certain end use applications that contain TPU specify that the TPU composition be halogen free. This has required TPU formulators to search for other flame retardants to replace the previously used halogen additives.
U.S. Pat. No. 6,777,466 assigned to Noveon IP Holding Co. discloses the use of melamine cyanurate as the only organic flame retardant additive in a thermoplastic polyurethane composition.
U.S. Pat. No. 5,837,760 assigned to Elastogram GmbH discloses a self-extinguishing flame retardant, thermoplastic polyurethane that contains one or more organic phosphonates and one or more organic phosphonates mixed with a melamine derivative.
U.S. Pat. No. 5,110,850 assigned to B.F. Goodrich Co. discloses halogen free flame retardant thermoplastic polymers where the sole flame retardant is a melamine that is free of melamine derivatives.
WO 2006/121549 assigned to Noveon, Inc. discloses a thermoplastic polyurethane containing a flame retardant combination including phosphinate compounds, phosphate compounds and a pentaerythritol and dipentaerythritol component.
WO 2012/067685 assigned to Lubrizol, Inc., discloses very similar thermoplastic polyurethane compositions. However the thermoplastic polyurethane compositions of the reference do not have high enough Limiting Oxygen Index (LOI) values and/or flame retardant properties to be useful in all applications.
Flame specifications for shipboard cables have become more stringent recently. There are currently no TPU-based products on the market that can pass the more demanding cable flame tests, such as CSA FT-4 for shipboard cables. Thus there is a need for TPU compositions and TPU-based products with improved high flame retardant properties, that would be suitable for such applications, while not impairing mechanical strength and processability of the TPU.
The LOI is a bench scale flame test used to assess the flammability of materials, including TPU compositions. It is a useful means of evaluating the relative flammability of various materials and can also help give some indication of how suitable a material may be for applications requiring high flame retardant properties. Thus there is a need for TPU compositions and TPU-based products with high LOI values, while not impairing mechanical strength and processability of the TPU.